There are a myriad number of applications in which an integrated circuit (IC) requires a constant current source (or reference current generator). These applications encompass both digital devices and analog devices. Many constant current sources are based on the principle of creating a constant voltage drop across a fixed on-chip resistor, thereby getting a constant current source. These types of constant current sources are suitable for most of the common application.
However, many applications require high precision and operate under extreme temperature conditions. One typical example is a cell phone, which typically includes high-precision components and must operate in sub-zero temperatures and in 100+ degree temperatures. For these types of applications, a constant current source based on a fixed on-chip resistor cannot be used. This is because the on-chip resistor is temperature sensitive. As the resistance increases with temperature, the current through the on-chip resistor must be reduced in order to maintain a constant voltage across the on-chip resistor. Thus, the supposedly constant current decreases with increasing temperature. This problem is often addressed by adding cooling equipment that maintains the integrated circuit in a narrow operating temperature range, thereby minimizing the variation in the desired constant current.
Therefore, there is a need in the art for improved constant current sources. In particular, there is a need for a reference current generator that is highly temperature insensitive across a relatively wide range of operating temperatures.